Take-all is a serious disease of cereals (wheat, barley, rye) which reduces the quality of the crops and the yields. In addition, it is an extremely difficult disease to detect because it can be confused with physiological shrivelling or with premature ripeness.
The agent responsible for this cryptogamic disease is Ophiobolus graminis. This fungus attacks and cankers both the radicular systems and the base of the stems of the cereals on which perithecia can form. The inoculum keeps well year after year, more especially in sensitive graminaceae, new growths and harvesting residues of diseased cereals. Accordingly, the infestation of a field persists for several years following an initial inoculation.
It would seem that dissemination of the inoculum during the primary infestation is caused by the transport of particles of soil or harvesting residues by agricultural machinery or even by wind. In any one field the parasite progresses from plant to plant either by the aerial route through ascospores or by the subterranean route through the mycelium. So far as the spread of the disease in a field is concerned, root-by-root propagation is the most prevalent form of propagation, its rate being determined both by the type of soil (extremely high in light, aerated and alkaline soil, becoming lower in heavy, acid soil or high-humus soil) and by the planting density.
Hitherto, various methods have been proposed for controlling this disease, including for example
ROTATION CROPPING,
ACCELERATION OF THE PROCESS BY WHICH HARVESTING RESIDUES ARE DEGRADED BY CULTURAL METHODS IN ORDER TO RESTRICT PERSISTENCE OF THE INOCULUM,
DEVELOPMENT OF A MICROFLORA TO COUNTERACT THE EFFECT OF THE FUNGUS,
SOWING IN SEED HOLES TO RESTRICT PROPAGATION OF THE DISEASE,
AND ABOVE ALL ROTATION CROPPING IN WHICH THE GROWING OF SENSITIVE CEREALS IS NOT OFTEN INCLUDED.
Unfortunately, none of these processes is completely effective, rather are they only palliatives whose object is to reduce the intensity of the disease and above all its effects, but not to treat it.
Accordingly, it is necessary to find a process for treating take-all from which immediate and substantial results can be obtained. The principal solutions considered in the past would appear to be either of a chemical nature (using phytochemical agents) or of a botanical nature by obtaining varieties of cereals resistant to Ophiobolus graminis, but unfortunately none of these possibilities would appear at present to be really practicable. Thus, if for example certain varieties of cereals are more likely to grow new roots, none of them would have a resistance level that could be exploited within the range of selection.